U.S. patent application number 16/772332 was filed with the patent office on 2021-04-22 for assembly consisting of a complex transparency device and at least one array of micro-images, as well as a security document comprising same.
This patent application is currently assigned to OBERTHUR FIDUCIAIRE SAS. The applicant listed for this patent is OBERTHUR FIDUCIAIRE SAS. Invention is credited to Xavier Borde, Jean-Louis De Bougrenet De La Tocnaye, Marie Dejean, Julien Gillot, Vincent Nourrit.
Application Number | 20210114398 16/772332 |
Document ID | / |
Family ID | 1000005347379 |
Filed Date | 2021-04-22 |
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United States Patent
Application |
20210114398 |
Kind Code |
A1 |
De Bougrenet De La Tocnaye;
Jean-Louis ; et al. |
April 22, 2021 |
Assembly Consisting Of A Complex Transparency Device And At Least
One Array OF Micro-Images, As Well As A Security Document
Comprising Same
Abstract
An assembly comprising a complex transparency device, i.e. a
refractive and/or diffractive device acting on the light phase, and
at least one array of micro-images, wherein: the complex
transparency device comprises a periodical two-dimensional array
formed from individual "pupils," wherein each pupil comprises a
micro-optical device, at least some of the micro-optical devices
having a non-centered optical axis, and at least some of the
micro-optical devices positioned non-periodically with variable
off-setting of the optical axis thereof with the array; the array
of micro-images comprising as many micro-images as micro-optical
devices; each micro-image has a contour identical to that of the
associated pupil and a surface which is at the most identical to
that of the associate pupil; and each micro-image is sub-divided
into at least one thumbnail image such that when the transparency
device is positioned facing the array of micro-images, and an
observer observes the array through the transparency device, the
observer sees, at least in a given direction of observation, an
image which is reconstructed by the combination of the thumbnail
images associated with the direction, wherein within the same
sub-division, certain thumbnail images, form "firsts group" and are
distributed such that when the transparency device is positioned
facing the array of micro-images, the thumb-nail images are
respectively arranged according to the optical axis of the
associated micro-optical device.
Inventors: |
De Bougrenet De La Tocnaye;
Jean-Louis; (Guilers, FR) ; Dejean; Marie;
(Brest, FR) ; Nourrit; Vincent; (Brest, FR)
; Gillot; Julien; (Chateaugiron, FR) ; Borde;
Xavier; (Osse, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OBERTHUR FIDUCIAIRE SAS |
Paris |
|
FR |
|
|
Assignee: |
OBERTHUR FIDUCIAIRE SAS
Paris
FR
|
Family ID: |
1000005347379 |
Appl. No.: |
16/772332 |
Filed: |
December 13, 2018 |
PCT Filed: |
December 13, 2018 |
PCT NO: |
PCT/EP2018/084669 |
371 Date: |
June 12, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B42D 25/328 20141001;
B42D 25/351 20141001; G02B 3/08 20130101 |
International
Class: |
B42D 25/328 20060101
B42D025/328; B42D 25/351 20060101 B42D025/351; G02B 3/08 20060101
G02B003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2017 |
FR |
1762169 |
Claims
1. An assembly comprising: a complex transparency device having a
refractive or diffractive device acting on the phase of the light
and, on the other hand, of at least one micro-image array, wherein:
said complex transparency device consists of a periodic
two-dimensional array formed of individual pupils in which each
pupil includes a micro-optical device, at least part of the
micro-optical devices having a non-centered optical axis and
positioned non-periodically with variable offsets of their optical
axis within said array; said micro-image array comprising as many
micro-images as there are micro-optical devices; each micro-image
has a contour identical to that of the associated pupil and a
surface identical to that of the associated pupil; each micro-image
is subdivided into one or more thumbnail images, so that when said
transparency device is positioned facing said micro-image array and
said array is observed through said transparency device, an image
reconstructed by the combination of the one or more thumbnail
images associated is observable at least along a given direction of
observation, and wherein within the one or more thumbnail images, a
first group of thumbnail images is distributed in such a way that
when said transparency device is positioned facing said micro-image
array, each thumbnail image of the first group of thumbnail images
is disposed along the optical axis of an associated micro-optical
device.
2. The assembly according to claim 1, wherein each of said
micro-optical devices has a non-centered optical axis and that all
said micro-optical devices are positioned non-periodically.
3. The assembly according to claim 1, wherein said pupils are of
identical shape and surface.
4. The assembly according to claim 1, wherein said micro-optical
devices (1) having a non-centered optical axis consist of Fresnel
lenses.
5. The assembly according to claim 1, wherein said micro-optical
devices having a non-centered optical axis consist of circular
blazed gratings.
6. The assembly according to claim 1, wherein each micro-image is
subdivided into at least two thumbnail images.
7. The assembly according to claim 1, wherein within the same
subdivision a second group of thumbnail images is distributed in
such a way that when said transparency device is positioned facing
said micro-image array, each thumbnail image of the second group of
thumbnail images are each disposed along the same axis, different
from the optical axis of said associated micro-optical device.
8. The assembly according to claim 1, wherein the image
reconstructed by the combination of the one or more thumbnail
images of each subdivision, seen from at least one predetermined
angle of observation, constitutes a recognizable information or has
a recognizable visual effect.
9. The assembly according to claim 1, wherein said complex
transparency device and said micro-image array are carried by the
same medium.
10. The assembly according to claim 1, wherein said complex
transparency device and said micro-image array are carried by
different media.
11. The assembly according to claim 8, wherein said two-dimensional
micro-image array is generated by a display device such as a
digital tool screen, whether it is mobile or not.
12. An apparatus, comprising: a first face and a second face
opposite the first face, wherein at least one of the first face or
second face carries a complex transparency device includes: a
periodic two-dimensional array formed of individual pupils in which
each pupil includes a micro-optical device, at least part of the
micro-optical device having a non-centered optical axis and
positioned non-periodically with variable offsets of their optical
axis within said array; wherein each micro-image array comprising
as many micro-images as there are micro-optical devices, wherein
each micro-image has a contour identical to that of the associated
pupil and a surface identical to that of the associated pupil,
wherein each micro-image is subdivided into one or more thumbnail
images, so that when said transparency device is positioned facing
said micro-image array and said array is observed through said
transparency device, an image reconstructed by the combination of
the one or more thumbnail images associated is observable at least
along a given direction of observation, and wherein within the one
or more thumbnail images, a first group of thumbnail images is
distributed in such a way that when said transparency device is
positioned facing said micro-image array, each thumbnail image of
the first group of thumbnail images is disposed along the optical
axis of an associated micro-optical device.
13. The apparatus according to claim 12, wherein the complex
transparency device extends above a printing carried by the first
or second face, this printing constituting the two-dimensional
micro-image array.
14. The apparatus according to claim 12, wherein the complex
transparency device extends through a window which opens on said
opposite faces, and wherein the complex transparency device further
includes a printing constituting the two-dimensional micro-image
array disposed relative to each other so that they can be
superimposed at least momentarily.
15. The apparatus according to claim 12, wherein said printing
consists of at least one ink chosen from the group consisting of
the following inks: visible black ink, colored ink, matt ink, gloss
ink, ink with iridescent effect, metallic ink, optically variable
ink, invisible ink but visible under ultraviolet radiation
(fluorescence or phosphorescence) or visible under infrared
radiation.
16. The apparatus according to claim 12, wherein the complex
transparency device is coated with a layer of transparent varnish,
so that the upper surface of said device is planar.
17. The apparatus according to claim 13, wherein said printing
consists of at least one ink chosen from the group consisting of
the following inks: visible black ink, colored ink, matt ink, gloss
ink, ink with iridescent effect, metallic ink, optically variable
ink, invisible ink but visible under ultraviolet radiation
(fluorescence or phosphorescence) or visible under infrared
radiation.
18. The apparatus according to claim 12, wherein the apparatus is a
security document.
19. The apparatus according to claim 18, wherein the security
document is a bank note.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an assembly consisting on
the one hand, of a complex transparency device, i.e. of a
refractive and/or diffractive device acting on the phase of the
light and, on the other hand, of at least one micro-image array. It
also relates to a security document such as a banknote which
includes such an assembly.
TECHNOLOGICAL BACKGROUND OF THE INVENTION
[0002] Various techniques exist for encoding information by optical
means in the field of security documents and, more particularly,
fiduciary documents such as banknotes.
[0003] The holographic-type technique is the oldest one. Holograms
on smart cards are still used, as described for example in document
WO9740464.
[0004] Similarly, the devices exploiting the Moire effect are
currently widely used. In this regard, reference can be made to
document EP2811470. They are based on a coupling between a phase
array (such as micro-optical devices) and a micro-image array, of
different pitches.
[0005] In addition, the techniques related to the principle of
auto-stereoscopy which favor some reading angles are also very
developed, as illustrated in document US2014/177008.
[0006] Variants combining the various aforementioned effects have
of course been proposed, in particular in document
WO2016/183635.
[0007] Other secondary techniques implementing more complex effects
such as those using the polarization (see for example
WO2016/141420) or resonance modes (for example with "plasmon
effect") are also proposed or generally reinforce an already
existing protection (see for example document WO2015/113718).
[0008] Finally, document WO 2017/184581 describes an assembly
according to the preamble of claim 1 of the present
application.
[0009] All these techniques, when applied to the security documents
such as the fiduciary documents, aim at making their unauthorized
reproduction particularly difficult, in other words at complicating
the task of the counterfeiters.
[0010] The present invention, which is based on the
multiscopic-type technique, aims at proposing a new variant which
is even more difficult to reproduce and which includes particularly
effective means for verifying the authenticity of the concerned
document.
SUMMARY OF THE INVENTION
[0011] Thus, the present invention relates to an assembly
consisting on the one hand, of a complex transparency device, i.e.
of a refractive and/or diffractive device acting on the phase of
the light and, on the other hand, of at least one micro-image
array, wherein:
[0012] said complex transparency device consists of a periodic
two-dimensional array formed of individual "pupils" in which each
pupil includes a micro-optical device, at least part of these
micro-optical devices having a non-centered optical axis, and at
least part of these micro-optical devices being positioned
non-periodically, i.e. with variable offsets of their optical axis
within said array;
[0013] said micro-image array consists of as many micro-images as
there are micro-optical devices;
[0014] each micro-image has a contour identical to that of the
associated pupil and a surface at most identical to that of the
associated pupil;
[0015] each micro-image is subdivided into at least one thumbnail
image,
[0016] so that when said transparency device is positioned facing
said micro-image array, and when an observer observes said array
through said transparency device, he sees, at least along a given
direction of observation, an image reconstructed by the combination
of the thumbnail images associated with this direction,
[0017] characterized by the fact that within the same subdivision,
some thumbnail images--i.e. only part of them, which constitute a
"first group"--are distributed in such a way that when said
transparency device is positioned facing said micro-image array,
these thumbnail images are each disposed along the optical axis of
said associated micro-optical device.
[0018] Furthermore, according to other non-limiting and
advantageous characteristics of the invention:
[0019] each of said micro-optical devices has a non-centered
optical axis and all of said micro-optical devices are positioned
non-periodically;
[0020] said pupils are of identical shape and surface;
[0021] said micro-optical devices having a non-centered optical
axis consist of Fresnel lenses;
[0022] said micro-optical devices having a non-centered optical
axis consist of circular blazed gratings;
[0023] each micro-image is subdivided into at least two thumbnail
images;
[0024] within the same subdivision, other thumbnail images, which
constitute a second group, are distributed in such a way that when
said transparency device is positioned facing said micro-image
array, these thumbnail images are each disposed along the same
axis, different from the optical axis of said associated
micro-optical device;
[0025] the image reconstructed by the combination of the thumbnail
images of each subdivision, seen from at least one predetermined
angle of observation, constitutes a recognizable information or has
a recognizable visual effect;
[0026] said complex transparency device and said micro-image array
are carried by the same medium;
[0027] said complex transparency device and said micro-image array
are carried by different media; and
[0028] said two-dimensional micro-image array is generated by a
display device such as a digital tool screen, whether it is mobile
or not.
[0029] The invention also relates to a security document, such as a
banknote, whose one of the opposite faces carries a complex
transparency device of the assembly according to any of the
preceding characteristics.
[0030] Advantageously:
[0031] said complex transparency device extends above a printing
carried by one of said opposite faces, this printing constituting
the two-dimensional micro-image array of said assembly according to
any of the preceding characteristics.
[0032] said complex transparency device extends through a window
which opens on said opposite faces and which includes a printing
constituting the two-dimensional micro-image array of said assembly
according to any of the preceding characteristics, this window and
this printing being disposed relative to each other so that they
can be superimposed at least momentarily.
[0033] said printing consists of at least one ink chosen from the
group consisting of the following inks: visible black ink, colored
ink, matt ink, gloss ink, ink with iridescent effect, metallic ink,
optically variable ink, invisible ink but visible under ultraviolet
radiation (fluorescence or phosphorescence) or visible under
infrared radiation.
[0034] said transparency device is coated with a layer of
transparent varnish, so that the upper surface of said device is
planar.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Other characteristics and advantages of the invention will
become apparent upon reading the following description of a
preferred embodiment of the invention. This description is made
with reference to the appended drawings wherein:
[0036] FIG. 1 is a diagram intended to illustrate the principle of
multiscopy;
[0037] FIGS. 2 and 3 are diagrams intended to illustrate cases of
auto-stereoscopy;
[0038] FIG. 4 is a diagram intended to explain how different images
are reconstructed from micro-images that extend under a lens
array;
[0039] FIG. 5 is a diagram showing the equivalence between the
combination of a refractive lens and of a prism on the one hand,
and a Fresnel lens whose optical axis is de-centered on the other
hand;
[0040] FIGS. 6A to 6D are diagrams intended to show the symmetry of
the mechanisms involved, namely the de-centering of the optical
axis of the lenses and the adaptation of the location of the
thumbnail image (image portion);
[0041] FIGS. 7A to 7C illustrate a particular embodiment of the
assembly according to the invention;
[0042] FIGS. 8 and 9 are top views of two alternative embodiments
of a portion of micro-lens arrays;
[0043] FIG. 10 is a diagram showing a banknote seen from above, and
whose one of the faces carries an assembly according to the present
invention;
[0044] FIG. 11A is a very schematic view, in section, of the
assembly of the preceding figure;
[0045] FIGS. 11B and 11C are views similar to FIG. 11A of
alternative embodiments;
[0046] FIG. 12 is a view similar to FIG. 10, the banknote being
provided with a transparent window which carries only one lens
array of said assembly, this figure also showing a phone on the
screen from which a micro-image array can be displayed;
[0047] Finally, FIG. 13 represents a banknote which includes, in a
first region, a transparent window which carries only one lens
array of said assembly and, in a second region, a printing of a
micro-image array.
DETAILED DESCRIPTION OF THE INVENTION
[0048] According to the present invention, an assembly is formed
consisting of two main elements, namely a complex transparency
device which is likely to appear on a security document such as a
banknote and which operates in transmission, consisting of
micro-optical devices, as well as a medium that the complex
transparency device is facing, by means of a simple alignment.
[0049] Preferably, this medium accommodates at the place where the
complex transparency device is superimposed, patterns that cannot
be interpreted with the naked eye which can be affixed directly on
the substrate of the medium (made of paper and/or polymer) or be
visible on the screen of a "smartphone"-type phone or of a touchpad
for example, and be readable in reflection or transmission.
[0050] Alternatively, part of the patterns may be on the substrate
of the medium and another part may be on the mobile appliance
described above. When these two elements are superimposed correctly
they allow:
[0051] either, forming different images, for a certain number of
given positions of observation (in near vision, i.e. in the
vicinity of 40 cm) so as to give an illusion of relief or
movement;
[0052] or, combining images into stereoscopic vision so as to allow
perceiving a color by colorimetric combination;
[0053] or forming a second image, in an accurate position of
observation, such that this second image is somehow hidden in the
main image.
[0054] A decryption is therefore implemented and is due to the
combination of two planes, that of an array of micro-images and
that of an array of micro-optical devices which are themselves
encrypted or encoded individually, i.e. whose arrangement of the
smallest constituent units, the micro-images reciprocally the
micro-optics, does not follow any rule of symmetry or replication
(translation), which is straightaway easy to recognize by simple
observation with the naked eye or assisted (magnifying glass,
microscope).
[0055] Alternatively, the combination of the two planes can be
fixed and made once and for all either directly on the substrate of
the medium or indirectly by means of another vector itself affixed
or integrated into the substrate of the medium (for example
elements transferred or hot-rolled or cold-rolled, partially
embedded wires, etc.).
[0056] Principle of Encoding and State of the Art Specific to the
Present Invention:
[0057] The system of the assembly according to the invention
resides in the combined encoding (encryption) medium +complex
transparency device. It is meant by "complex transparency device"
any refractive, diffractive or combined device, acting on the phase
of the light (for example diffractive gratings, lenses, prisms,
etc.).
[0058] Each image of the medium consists of "thumbnail images"
corresponding to sub-elements of a micro-image array (ultimately,
the smallest thumbnail image is the pixel of the image itself).
[0059] The principle of multiscopy is to present to the vision
different images according to the inclination and to the
orientation of the gaze.
[0060] The best known are the use of parallax barriers or of
lenticular arrays. The present invention here draws inspiration
therefrom by generalizing it.
[0061] Indeed, the assembly according to the invention consists of
a two-dimensional refractive grating behind which a micro-image
array is placed, each thumbnail image may be offset relative to the
optical axis of the lens which is directly opposite thereto for the
purposes of formation of independent images.
[0062] In the past, many achievements of this type have already
been proposed. Thus, for example, according to document
US2014/177008, by tilting the device, it is possible to see an
image moving, movements of objects that move relative to each other
or effects of relief, shapes, appearance/disappearance, zoom. For
this, portions of images (each corresponding to a viewing angle)
are arranged in a very particular manner under each lens.
[0063] Similarly, in document WO2015011493, a different image per
viewing angle is involved (the difference being that the portions
of images placed under the center of the lenses are larger than
those placed on the sides, because the angle range perceived in the
center of the lenses is larger).
[0064] Definitions:
[0065] Throughout the present application, the following terms and
expressions have the definitions given below:
[0066] Micro-optical device: it is formed of a device whose size
can vary between 25 .mu.m and 100 .mu.m. Its focal length can vary
between 10 and 400 .mu.m and preferably between 40 .mu.m and 100
.mu.m.
[0067] Micro-image array: It is formed of thumbnail images whose
size is greater than 2 .mu.m and which are magnified under the
effect of micro-optical devices. This accordingly allows forming a
large image.
[0068] Image: the image is what is perceived when looking through
an array of micro-optical devices. Its size corresponds to the size
of said array, i.e. between a few square millimeters and a few
square centimeters. It is formed of a set of thumbnail images
(otherwise called image portions).
[0069] Thumbnail image or image portion: a thumbnail image is the
smallest sub-element of the micro-image array and which will
constitute an image. Its size is smaller than or equal to that of a
micro-optical device. This allows having several possible thumbnail
images for a given device. Thus, the thumbnail image selected by a
micro-optics will be different depending on the viewing angle,
which will create a different image. Between two consecutive
images, the viewing angle can vary by a few degrees.
[0070] Principles Underlying the Present Invention:
[0071] The first principle implemented is based on three distinct
elements.
[0072] The first one concerns the nature of the refractive grating
disposed above the micro-image array. By taking inspiration from
the multiscopic principle, it is proposed here to combine an
imaging function (lens or an axicon) with a prism-type deflection
function, and this individually and independently for each element
of the grating. Under these conditions, the refractive grating
advantageously consists of a micro-optical device including an
imaging element (a lens or an axicon) coupled to a prism (whose
angle and orientation are fixed).
[0073] The second one is based on the design of the array of
micro-images. The latter are disposed and designed so that placing
them facing the optical element creates, at some positions of the
gaze, different images.
[0074] The third one concerns the phase aliasing of the
micro-optical devices. Indeed, this phase aliasing allows merging
the imaging function with the prism function by transforming it
into a function of translation of the axis of the imaging object
relative to the optics. This aliasing simplifies the manufacture of
the optics and the implementation of the second element.
[0075] The second principle, i.e. the fact that the array of
micro-optical devices is not necessarily periodic, makes it more
difficult to copy the array if the latter is not covered with a
compensation layer, such as a varnish aiming at making the surface
of the array inaccessible. If this compensation layer is not
present, thanks to the invention, the arrangement of the smallest
constituent units of the latter indeed cannot be deduced by simple
observation.
[0076] In addition to resorting to the principle of aliasing of the
considered optics, both the translations of the imaging optics
(made possible by the aliasing) and respectively the thumbnail
images are encoded in an apparently collectively random manner, so
as to avoid the easy decryption and, consequently, to be able to
reproduce it only by a hypothetical faithful copy not deduced from
a simple observation.
[0077] The device making it possible to reconstruct various images
at a certain number of positions of the gaze leading to a
configuration of micro-optics and associated thumbnail images is
therefore randomly cross-connected, which presupposes a
recalculation of the deflections resulting from this
cross-connection in order to preserve the conditions of the initial
imagery.
[0078] The result is a distribution of the translations of the
micro-optics which is no longer even and therefore much more
difficult to deduce and/or reproduce.
[0079] In practice, this cross-connection is made with a maximum
deflection constraint limited by the manufacturing constraint upon
calculation of the phase mask. For example, in the case of a
p-order Fresnel lens, the limit is reached when the phase deviation
between 2 consecutive pixels of the edge of the mask (i.e. the
greatest spatial frequency) is greater than p.pi.. Beyond that, it
becomes a sub-sampling.
[0080] FIG. 1 illustrates the principle of multiscopy. Thus, a
converging lens LC is involved here, so that different images for
different viewing angles can be seen. For the viewing angle AV1,
only the image portion PI1 is seen, since the converging lens
concentrates the rays. On the other hand, for the viewing angle
AV2, only the image portion PI2 will be seen. It is thus possible
to have an alternation between different images.
[0081] FIGS. 2 and 3 illustrate cases of use of auto-stereoscopy.
Thus, with reference to FIG. 2, a lenticular array RL is involved,
which as explained above, allows favoring some viewing angles AV1
and AV2, so that a thumbnail image IG portion will be visible for
each eye. Under these conditions, it will look like it is a relief
image. In the same way and with reference to FIG. 3, it is possible
to use the parallax barriers BP which block portions of beams so
that each eye can see different thumbnail images IG.
[0082] In FIG. 4, there is a micro-image array MI1 to MI4 in the
central position. Each lens of the lens array RL is delimited by a
square under which extend four micro-images which are disposed so
that they reconstruct a large image GI1 to GI4 for four given
viewing angles AV1 to AV4.
[0083] Referring to FIG. 5, there is the equivalence between the
combination of a refractive lens LC (optical power) and of a prism
P (deflection of the light) on the one hand, and a de-centered
Fresnel lens LF on the other hand. The latter has the same effects,
namely concentration and deflection of the light. The advantage is
that the deflection results in a translation.
[0084] Although this is not represented in the appended figures, an
axicon associated with a prism is also equivalent to a de-centered
circular blazed grating ("axicon phase hologram").
[0085] FIGS. 6A to 6D show both the effect of the de-centering of
the optical axis of a lens and the adaptation of the thumbnail
image (or image portion) in order to see or not the latter through
the lens depending on the desired viewing angle. In the case of
FIG. 6A, the image portion PI is perceived for the viewing angle
AV1 when the lens is centered.
[0086] However, if the lens is de-centered towards the right, the
image portion PI is then seen for the viewing angle AV2 (case of
FIG. 6B), which amounts to moving the image portion PI to the left,
in the case of the centered lens, as shown in FIG. 6C. in order to
be equivalent to the case of FIG. 6A with a de-centered lens, it is
then also necessary to move the image portion PI, as shown in FIG.
6D.
[0087] It is seen that these functionalities can be combined (i.e.
interlaced) to make the extraction of the constituent parameters of
the concerned arrangement more difficult.
[0088] FIGS. 7A to 7C represent a particular exemplary embodiment
of an assembly according to the present invention.
[0089] Thus, FIG. 7A represents a complex transparency device which
consists of a two-dimensional periodic array RPU formed of
individual "pupils" PU, i.e. here square-shaped locations, in which
each pupil PU includes a micro-optical device. For reasons of
readability of the figure, the contour of each pupil PU is
represented here, but in reality it is not visible.
[0090] Still for reasons of ease of reading, this figure represents
only the optical center 10 of lenses 1 placed on this array. It can
be observed that these lenses have variable offsets from their
optical center within the array.
[0091] In FIG. 7B, the aforementioned array RPU still appears, but
now only micro-images 2 are represented, with some thumbnail images
20 represented by a black square. These thumbnail images constitute
only part of the totality of the thumbnail images and constitute a
"first group". It will be noted that their distribution is also
non-periodic. However, the position of some of them coincides with
those of the optical centers identified in FIG. 7A.
[0092] FIG. 7C represents the "final situation", i.e. the one in
which the two arrays are superimposed.
[0093] At the sight of an observer, a generally "O"-shaped symbol
represented in gray in the figure then appears, provided that the
direction of the gaze is normal to the plane of the arrays. This
"O" is an image reconstructed by the combination of the thumbnail
images 20 of FIG. 7B.
[0094] And for the pixels not belonging to the symbol, the
thumbnail images are far from the center of the lenses.
[0095] If the lens array of FIG. 7A or the thumbnail image array of
FIG. 7B is taken separately, there is no information because their
distributions both seem random and unrelated. It is only the
combination of the two that shows the information constituted by
the aforementioned symbol.
[0096] Although this is not represented here, a second symbol could
be disclosed (or even additional symbols), provided that the
thumbnail images corresponding thereto are all visible together
along another axis of observation.
[0097] Thus, these thumbnail images (different from those of the
aforementioned "first group") constitute a "second group" of
thumbnail images.
[0098] In this way, the observer will observe the presence of the
aforementioned "O" if the direction of his gaze is normal to the
plane of the arrays. Then, by orienting his gaze along a different
direction (or by modifying the orientation of the assembly), he
will disclose the second symbol.
[0099] Finally, for all other directions, no symbol will be
disclosed.
[0100] FIGS. 8 and 9 represent two micro-lens arrays 1 which have
been generated independently of each other and in a random manner.
For each of the micro-lenses, the micro-images placed below are
adapted accordingly. Despite the difference between the two arrays,
it is possible to create a combination of the lenses-thumbnail
images dispositions such that exactly the same visual effect (for
example, a growing square) is obtained.
[0101] It is observed that the uneven distribution of the lenses
prevents reproduction other than by recopying of the particular
arrangement, this arrangement can vary endlessly.
[0102] The addition of a hidden symbol in the arrays allows
identifying that the pattern made is not a forgery of the
original.
[0103] This symbol can be, for example, a second image only
observable at a given angle (and therefore hidden for all the other
angles of observation) or even, an observable pattern in reflection
on the surface of the lenses and linked to their arrangement.
[0104] It may for example be a finite set of lenses whose optical
axis is offset in an orderly manner in the non-periodic array to
form characters or patterns. The observation of these lenses from a
given angle (rather large so as not to see the thumbnail images)
would allow recognizing the characters or the patterns.
[0105] Advantageously, the assembly E of the present invention is
carried by a security document such as a banknote.
[0106] Such a banknote 3 has been represented very schematically in
FIG. 10. On one of its opposite faces, it carries said assembly
E.
[0107] As shown more specifically in the embodiment of FIG. 11, the
assembly E here consists of a lens array 1 and a micro-image array
2 carried by the face 30 of the banknote.
[0108] The assembly E can be made in this case in two steps, not
necessarily consecutive, directly on the substrate of the banknote
3.
[0109] The assembly E can also be an insert which has become
attached to the banknote 3 after an application step (for example
in the form of a hot or cold transfer film, a hot or cold rolled
film, etc.) or an integration step, as illustrated in FIG. 11B
which shows in section a safety wire carrying the assembly E, wire
inserted in the mass of the substrate but with windows making it
possible to observe it with the naked eye on the surface at some
places).
[0110] Finally, the assembly E may be passing through the substrate
(as shown in FIG. 11C) constituting the banknote 3 (if it consists
for example of a transparent polymer opacified in some places,
except facing the array 1).
[0111] As regards the micro-image array 2, it then consists of the
recognizable result of any technique making it possible to
constitute, in the form of images, shapes, patterns, information,
for example and without this being limiting by printing,
metallization/demetallization, laser engraving.
[0112] To retain only the printing technique, the latter is carried
out according to any known method making it possible to apply at
least one ink chosen from the group consisting of the following
inks: visible black ink, colored ink, matt ink, gloss ink, ink with
iridescent effect, metallic ink, optically variable ink, invisible
ink but visible under ultraviolet radiation (fluorescence or
phosphorescence) or visible under infrared radiation.
[0113] Furthermore, the lens array 1 extends above the printing,
either permanently or momentarily.
[0114] This lens array can for example be engraved in a first step
in a photosensitive resin such as the resin S1813 (supplier
Shipley) by photolithography.
[0115] The following can be made for its origination.
[0116] A resin layer is deposited on a glass substrate. The
resinated plate is then exposed to a laser beam in the UV, which is
modulated by a mask corresponding to the phase mask to be engraved.
After development, the areas of the mask which have been exposed
are removed (in the case of a "positive" resin, otherwise it is the
non-exposed parts that are removed). This is how the plate is
engraved in relief, the maximum engraving depth increasing with the
exposure time.
[0117] From this origination, a replication process follows to
obtain the tools and then the resulting finished product, i.e. the
lens array 1, either directly on the banknote 3, or in a shape that
can be integrated thereto (attached insert after application or
integration) or even in the shape that exploits the transparency of
the constituent substrate (case of the banknote made of polymeric
substrate mentioned above).
[0118] Finally, there is also a variant in which this lens array 1
is removable and not attached to the banknote 3 and, in this case
only, the array 2 is permanently carried by the banknote.
[0119] Preferably, the non-planar upper face of the lens array is
coated with a transparent varnish, so as to make it planar and to
avoid any fraudulent attempt of reproduction by direct
fingerprinting.
[0120] Once manufactured, the array is applied to the printing
implemented above.
[0121] In the embodiment of FIG. 12, the banknote 3 includes a
window 4. This window is attached to the rest of the banknote in
the case of a transparent substrate (for example banknote based on
bi-oriented polypropylene). When the substrate is opaque (for
example cotton fiber-based banknote), this window consists of an
opening obturated by a transparent polymer material, the latter
accommodating the lens array 1.
[0122] As for the micro-image array, it can be displayed on the
screen 50 of a smartphone-type phone 5 or on the digital-display
screen of a digital tool, whether it is mobile or not.
[0123] Thus, by opposing the window and the array displayed on the
screen, it is possible to proceed to the verification of the
authenticity of the banknote, depending on whether a recognizable
information is disclosed or not, or on whether a recognizable
visual effect is highlighted or not.
[0124] In the embodiment of FIG. 13, the arrays 1 and 2 are
disposed in two different regions of the banknote 3, so that by
aliasing this banknote as shown by the arrow f, the two arrays can
be superimposed to disclose a recognizable information or visual
effect.
[0125] In one embodiment not represented, a banknote such as the
one of FIG. 12 could be involved, in which the window carries, in
addition to the lens array, only part (for example half) of the
micro-image array, while the complementary part is displayed on the
screen of a phone or the like.
[0126] Finally, in an ultimate embodiment not represented, there
could be a banknote 3 that carries only the micro-image array 2 and
the lens array 1 would be built on a removable medium and added
only temporarily for the purposes of an authentication.
* * * * *